Lectures on Medical Biophysics
Department of Biophysics, Medical Faculty,
Masaryk University in Brno
Nuclear medicine and radiotherapy
Lectures on Medical Biophysics
Department of Biophysics, Medical Faculty,
Masaryk University in Brno
3
Nuclear medicine and radiotherapy
In this lecture we deal with selected methods of nuclear medicine and
radiotherapy including their theoretical background:
Nuclear medicine
➢Tracing
➢Radioimmunoassay
➢Simple metabolic examinations
➢Imaging
Radiotherapy
➢Sources of radiation – radioactive and non-radioactive
➢ Methods of radiotherapy
Radioactive decay
Interactions of ionising radiation with matter
Biological effects of ionising radiation
4
Radioactivity
• Radioactivity or radioactive decay is the
spontaneous transformation of unstable nuclei
into mostly stable nuclei. This is accompanied by
the emission of gamma photons, electrons,
positrons, neutrons, protons, deuterons and alpha
particles. In some transformations, neutrinos and
antineutrinos are produced. Unstable nuclei can be
found naturally or created artificially by
bombarding natural stable nuclei with e.g. protons
or neutrons.
• Radioactive decay has a stochastic character: it is
not possible to determine which nucleus will decay
at what time.
5
Nuclear medicine
Nuclear medicine
➢Tracing
➢Radioimmunoassay
➢Simple metabolic examinations
➢Imaging
6
Tracing and radioimmunoassay
➢Tracing: radionuclide is administered into body and its
physiological fate is monitored. Radioactivity is measured in
body fluids or tissue samples. Compartment volumes – e.g.
free water, blood, fat etc. – are often determined. We administer
defined amount (known activity) of a radionuclide, and determine its
concentration in taken samples after certain time. Then is possible to
calculate what is the volume, in which the radionuclide is present.
➢Radioimmunoassay (RIA) is a method of clinical
biochemistry and haematology. It is used for determination of
low concentrated substances, e.g. hormones in blood.
Radionuclide is applied outside the body and the antigen-antibody
interaction is studied in vitro. The antigen is labelled by radionuclide.
In RIA and tracing, mainly b-emitters are used (tritium,
iodine-125, iron-59 etc.), because the detector can be very
close to the radioactive sample.
Nuclear medicine
7
Devices for detectionScintillation
counter and scintigraphy
➢ Scintillation counter consists of a scintillation detector, mechanical parts and a lead collimator. The
collimator enables the detection of radiation only from a narrow spatial angle, in which the examined
body part is located. Signals of the detector are amplified, counted and recorded.
➢ Scintigraphy is used mostly for examination of kidneys and thyroid gland – by means of gammaemitters:
iodine-131 or technetium-99m. Tc-99m has a short half-life (6 hours vs. 8 days in I-131).
Technetium is prepared directly in dept. of nuclear medicine in technetium generators.
➢ Iodine used for thyroid is administered as KI, for kidneys we use technetium-labelled DTPA (diethylentriamin-penta-acetic
acid). Tc-99m is almost an ideal radionuclide – fastly excreted, short half-life,
almost pure gamma rays. (Iodine-131 produces also b-particles which increases radiation dose without
any benefit).
Nuclear medicine
8
The gamma camera, also called a scintillation camera or Anger
camera, is a device used to detection and image gamma radiation
emitting radioisotopes, for example during scintigraphy examination
The Gamma Camera
Gama camera consist of:
•collimator
•detector (scintillator and photomultiplier)
•mechanical elements
•compurter support
schema of Gamma Camera
9
The Gamma Camera
thin
(about 1.5
cm) NaI
phosphor
crystal
photomultiplier
tubes
(now being
replaced by a flat
digital sensor)
parallel hole
Pb (lead)
collimator
for
localisation
MCA
10
The Gamma Camera
11
Gamma-camera
➢ The digital sensor /
photomultiplier signals carry
information about the position of
the scintillation events.
However, a defined point on the
crystal has to correspond with
defined point of the examined
body part – we obtain an image
of radionuclide distribution in
the body. This can be achieved
only by collimators.
Nuclear medicine
with collimators
without collimators
sc. crystal
A collimator is a device that narrows a
beam of particles or waves. Contains
plates (lamellas) organized in planar
position.
12
Gamma-camera
• Anger cameras show the radionuclide
distribution very quickly. Therefore they
can be used for observation of fast
processes, including blood flow in
coronary arteries. They can also move
along the body. Physiologic (functional)
information is obtained or metastases
found (if the radionuclide is entrapped
there - iodine-131 or technetium-99m).
A whole body scan
showing metastases
of a bone tumour
Siemens company
13
SPECT – single photon emission
computed tomography
• Photons of radiation are detected from various directions, which
allows reconstruction of a cross-section.
• Most frequent arrangements and movements of detectors:
➢ Anger scintillation camera revolves around the body.
➢ Many detectors are arranged around the body in a circle or
square. The whole system can revolve around the body in a
spiral (helix).
Nuclear medicine
Special diagnostic imaging technique that uses
radionuclides and their detection.
14
Principle of SPECT
An object with a radiation source Z is surrounded by
scintillation detectors F with collimators K. The collimators
allow detection only of gamma-rays falling normally onto the
detector blocks. It enables us to localise the source of rays.
In SPECT, common
sources of radiation
(iodine-131,
technetium-99m) are
used.
Nuclear medicine
15
SPECT – images
http://www.physics.ubc.ca/~mirg/home/tutorial/applications.html#heart
Perfusion of heart in different
planes. „Hot“ regions are well
blood supplied parts of the heart
Brain with „hot“
regions
Nuclear medicine
16
SPECT – images
17
PET - positron emission tomography
➢ In PET, positron emitters are used. They are prepared in accelerators,
and their half-lives are very short – max. hours. For that reason the
examination must be done close to the accelerator, in a limited number of
medical centres.
➢ The positrons travel only very short distance, because they annihilate with
electrons forming two gamma photons (0.51 MeV), which move in
exactly opposite directions. These photons can be detected by two
opposite detectors connected in a coincidence circuit. Voltage pulses are
recorded and processed only when detected simultaneously in both
detectors. Detectors scan and rotate around the patient's body.
➢ The spatial resolution of PET is substantially higher than in SPECT. The
positron emitters are attached to e.g. glucose derivatives, so that we can
obtain also physiological (functional) information. PET of brain
visualises those brain centres which are at the moment active (have
increased uptake of glucose). PET allows to follow CNS activity on the
level of brain centres.
Nuclear medicine
18
PET principle
Explanation of the high spatial resolution of PET: The opposite
detectors in a coincidence circuit. A source of radiation Z is detected only
when lying on a line connecting the detectors. Detector A but not the
detector B can be hit through a collimator from the source Z2, because
this source is outside the detection angle of B. In SPECT, the signal
detected by A from Z1 would be partially overlapped by the signal coming
from source Z2.
Nuclear medicine
19
Functional PET of brain
http://www.crump.ucla.edu/software/lpp/clinpetneuro/lggifs/n_petbrainfunc_2.html
resting
Music – a non-verbal
acoustic stimulus
Visual stimulus
Nuclear medicine
20
intensive thinking
remembering a
picture
skipping on left leg
Nuclear medicine
21
Brain tumour - astrocytoma
Nuclear medicine
FDG – fluorodeoxyglucose, F-18
22
Radiotherapy
➢Sources of radiation
– radioactive
- non-radioactive
➢Methods of radiotherapy
23
Sources of radiation - radioactive
➢ Artificial radionuclides are used. The source is in direct contact with a tissue
or is sealed in an envelope (open or closed sources).
➢ The open sources:
– (1) Can be applied by metabolic way. Therapy of thyroid gland tumours by
radioactive iodine I-131, which is selectively captured by the thyroid.
– (2) Infiltration of the tumour by radionuclide solution, e.g. a prostate tumour by
the colloid gold Au-198. This way of application is seldom used today as well.
– Radioactive iodine uptake test is a type of nuclear test performed to evaluate thyroid
function. The patient ingests radioactive iodine (I-123 or I-131) capsules or liquid. After a
time (usually 6 and 24-hours later), a gamma probe is placed over the thyroid gland to
measure the amount of radioactivity in the thyroid gland. The values are then compared.
The same principle is used for therapy due accumulation of Iodine in thyroid
Radiotherapy
24
➢ The closed sources are more widely used today:
– (1) Needles with a small amount of radioactive substance. They
usually contain cobalt Co-60 or caesium Cs-137. The needles are
applied interstitially (directly into the tumour) - brachytherapy
– (2) The sources are also inserted into body cavities (intracavitary
irradiation).
– (3) Large irradiation devices (‘bombs’) for teletherapy. The
radionuclide is enclosed in a shielded container. The radioactive
material is moved into working position during irradiation. The most
commonly used are cobalt Co-60 or caesium Cs-137.
Sources of radiation - radioactive
prostate brachytherapy
25
Brachytherapy
• Brachytherapy is treatment, when the radioactive sources are applied
interstitially (directly into the tumour). Usualy by using needles or by
afterloader.
catheters in place
Afterloader
Each of the catheters is connected to a corresponding port on the afterloader. This
machine contains a single highly radioactive pellet at the end of a wire. The pellet is
pushed into each of the catheters one by one under computer control. The computer
controls how long the pellet stays in each catheter (dwell time), and where along the
catheter it should pause to release its radiation (dwell positions).
afterloader machine
26
Afterloader
made by Blessing-Cathay works with Ir-192. It is not only for
brachytherapy, it can be use as an instrument for safe intracavitary
irradiation
main unit
applicators
phantom
Control unit
Radiotherapy
27
„The cobalt bomb“
In 1951, Canadian Harold E. Johns used cobalt-60 for therapy
first.
Radiotherapy
Cobalt-60 unit „bomb“
28
Museum - University of Saskatchewan
29
„The cobalt bomb“
http://www.cs.nsw.gov.au/rpa/pet/RadTraining/
Radiotherapy
30
Leksell Gamma Knife
➢ 1951 – idea of radiosurgery by L. Leksell of Sweden
➢ The Leksell Gamma Knife is used for treatment of some
brain tumours and other lesions (aneurysms, epilepsy etc.)
➢ 201 Co60 sources are placed in a central unit with diameter of
400 mm in 5 circles, which are separated by the angle of 7,5
deg. Each beam is collimated by a tungsten collimator with a
conical channel and a circular orifice (4, 8, 14 a 18 mm in
diameter). The focus is in the centre where all the channel
axes (beams) intersect. The beams converge in the common
focus with accuracy of 0.3 mm.
➢ The treatment table is equipped by a movable couch. The
patient‘s head is fastened in the collimator helmet. It is
attached to the couch, which can move inside the irradiation
area.
Radiotherapy
31
Leksell Gamma Knife
Radiotherapy
32
Leksell Gamma Knife
➢ A Leksell stereotactic coordinate frame is attached to
patient‘s head by means of four vertical supports and
fixation screws. The head is so placed in a 3D
coordinate system, where each point is defined by
coordinates x, y, z. Their values can be read on the
frame. The target area can be located with an accuracy
better than ± 1 mm.
➢ A radiological image of the lesion is transferred to the
planning system which calculates the total dose from all
the 201 sources. By connecting of points with the same
dose a curve – isodose – is constructed. The borders of
treated lesion should correspond with isodose showing
50-70% of dose maximum. The isodoses copy precisely
the outlines of the pathologic lesion in tomographic
scans.
Radiotherapy
33
Leksell Gamma Knife
Radiotherapy
34
Leksell Gamma Knife
Radiotherapy
35
Radiation sources – non-radioactive
A) X-ray tube devices: Therapeutic X-ray tubes differ in construction from diagnostic Xray
tubes. They have larger focus area, robust anode and effective cooling. They are
(were) produced in three sorts:
– low-voltage (40 - 100 kV) for contact surface therapy. The radiation is fully
absorbed by a soft tissue layer 2 - 3 cm thick.
e.g., Chaoul lamp.
– medium-voltage (120 - 150 kV) for brachytherapy – from distance of max. 25cm.
They were used to irradiate tumours at max depth 5 cm.
– ortho-voltage (160 - 400 kV) for teletherapy (deep irradiation from distance). These
have been replaced by the radionuclide sources and accelerators.
B) Electron Accelerators: X-rays with photon energy above 1 MeV and g-radiation with
photon energy above 0,66 MeV are used for megavoltage therapy. Their sources are
mainly electron accelerators. The accelerated electrons are usually not used for direct
irradiation but the production of high-energy X-rays.
Radiotherapy
36
The linear accelerator
CLINAC 2100C in Masaryk memorial institute of oncology in Brno
Radiotherapy
37
The linear accelerator
http://www.cs.nsw.gov.au/rpa/pet/RadTraining/MedicalLinacs.htm
Radiotherapy
38
The linear accelerator
http://www.cs.nsw.gov.au/rpa/pet/RadTraining/MedicalLinacs.htm
Radiotherapy
high velocity of electrons
(due magnetic acceleration)
= high energy of X ray beam
39
The cyclotron
Z – source of the
accelerated particles
(protons),
D1 and D2 – duants or
dees,
G - generator of highfrequency
voltage.
Radiotherapy
m
qB
f
.2
.

=
40
The cyclotron
http://www.aip.org/history/lawrence/first.htm
1933 – one
of the first
cyclotrons in
background
Ernest O. Lawrence
(1901-1958)
Radiotherapy
41
The cyclotron in
oncology – proton
(hadron) therapy
The Sumitomo cyclotron
Radiotherapy
42
Hadron radiotherapy
Hadrons (protons and light ions) lose their energy mainly in collisions with nuclei and electron shells.
The collisions with electrons are dominant for energies used in radiotherapy. The energy deposited is
indirectly proportional to the second power of hadron velocity. It means practically that the hadrons
deposit most of their energy shortly before end of their tracks in the tissue. This fact is exploited in
hadron therapy because (in contrary to the conventionally used photons) the tissues lying in front of the
Bragg peak receive a much smaller dose compared with the target area. The tissues behind the target
are not irradiated. The target can be precisely determined and thus damage to the surrounding healthy
tissue is minimised. The Bragg peak area is given by energy of the particle. In therapy, the necessary
penetration depth is about 2 – 25 cm, which corresponds to an energy of 60 – 250 MeV for protons and
120 – 400 MeV for light ions.
Radioterapie
focusing of absorbed dose
43
Radiotherapy planning for X-ray beams
After tumour localisation, the radiotherapist determines the best way of
irradiation in co-operation with a medical physicist. The tumour has to
receive maximum amount of radiation but the healthy tissues should be
irradiated minimally and some should be totally avoided. When
irradiating the tumour from only one side, the tissues in front of it would
receive higher dose than the tumour and the near side of the tumour
more than the far one. That is why irradiation is performed from different
directions. The skin area, through which the radiation beam enters the
body, is called the irradiation field; irradiation from different directions
(2, 3, 4) is called multi-field treatment. In some cases (tumours of
oesophagus and prostate) the multi-field treatment is replaced by
moving beam treatment – the source of radiation moves above or
around the patient in circle or arc (tumour-centred) during irradiation.
The radiotherapeutic plan involves the energy of radiation, daily and
total dose of radiation, number of fractions etc.
Radioterapie
44
Simulator
X-ray simulator is an XRI device
having the same geometry as
the accelerator. It is used to
locate the target tissues which
should be irradiated. To ensure
always the same patient
positioning both in the simulator
and the accelerator, there is a
system of laser lights in the
room. An identical system of
laser beams is used in the
accelerator room.
Radiotherapeutic simulator Acuity
Radioterapie
45
For irradiation of surface tumours, we have to use radiation of low
energy, for deep tumours, the energy must be substantially higher.
In radiotherapy, mainly X-ray sources are used (the accelerators for the
so-called megavoltage therapy) as well as the cobalt-60 g-radiation
sources. The radiation dose is optimised by means of simulators. To
achieve maximum selectivity of deep tumour irradiation, the
appropriate irradiation geometry must be applied:
➢ Focal distance effect. Intensity of radiation decreases with the
square of source distance. The ratio of surface and deep dose is
higher when irradiating from short distance. Therefore, surface lesions
are irradiated by soft rays from short distances (contact therapy,
brachytherapy). Deep tumours are treated by penetrating radiation
from longer distance (teletherapy).
➢ Irradiation from different directions or by a moving source. The lesion
must be precisely localised, the irradiation conditions must be
reproducible. Advantage: The dose absorbed in the lesion (tumour) is
high – radiation beams intersect there. Dose absorbed in surrounding
tissue is lower.
Geometry of irradiation
Radiotherapy
46
Geometry of irradiation
The effectiveness of
repair processes in
most normal tissues is
higher than in tumours.
Therefore, partition of
the therapeutic dose in
certain number of
fractions or use of
„moving beam
treatment“ spares the
normal tissue.
„moving beam
treatment“
Radiotherapy
47
theoretical knowledge of radioation
48
Laws valid for radioactive decay
➢Law of mass-energy conservation
➢Law of electric charge conservation
➢Law of nucleon number conservation
➢Law of momentum conservation
Radioactive decay
49
Law of radioactive decay
The activity A of a radioactive sample at a given time (i.e,
the number of nuclei disintegrating per second, A = dN/dt)
is proportional to the total number of undecayed nuclei
present in the sample at the given time:
 is the decay or transformation constant
Units of A are becquerel (Bq) [disintegrations per second, s-1]
(in the past: curie, 1 Ci = 3.7 x 1010 Bq)
The negative sign indicates that the number of undecayed nuclei is
decreasing.
Radioactive decay
= A
50
This equation is solved by integration:
Nt = N0.e-.t
A more useful equation for nuclear medicine
and radiotherapy is (obtained by dividing the
above equation by dt on both sides):
At = A0.e-.t A is activity
Radioactive decay
51
Physical half-life
➢Tf – time in which the sample activity At
decreases to one half of the initial value
A0. Derivation:
A0/2 = A0.e-.Tf thus ½ = e-. Tf
➢taking logarithm of both sides of the
equation and rewriting:
Tf = ln2/f thus Tf = 0,693/f
Radioactive decay
52
Biological and effective half-life
➢ Tb – biological half-life – time necessary for the
physiological removal of half of a substance from
the body
➢ b – biological constant – relative rate of a
substance removal
➢ Biological and physical processes take place
simultaneously. Therefore, we can express the Tef –
effective half-life and
ef – effective decay constant
➢ The following equations hold: ef = b + f and
1/Tef = 1/Tf + 1/Tb ,
thus
Radioactive decay
bf
bf
ef
TT
TT
T
+
=
.
53
Technetium generator
An example of practical
importance of the
radioactive equilibrium in
clinical practice –
production of technetium
for diagnostics: Mo-99
half-life is 99 hrs., Tc-99m
half-life is 6 hrs.
During radioactive decay, a daughter radionuclide is
produced. In cases when the half-life of the parent
radionuclide is much longer than the half-life of the daughter
radionuclide both parent and daughter end up with the same
activity (radioactive equilibrium).
Radioactive decay
1N1 = 2N2
54
Classes of radioactive decay
a (alpha) decay
Seaborgium transforms in rutherfordium. Helium nucleus
– a particle – is liberated. Daughter nucleus recoils as a
consequence of the law of momentum conservation.
(http://www2.slac.stanford.edu/vvc/theory/nuclearstability.html)
Radioactive decay
55
Classes of radioactive decay
b (beta) decay = emission
of an electron or positron K-capture
b decay is an isobaric transformation in which besides the b particles
are formed also neutrinos (electron antineutrino or electron neutrino
ne). nucleon number is not changed.
Radioactive decay
56
Classes of radioactive decay
g (gamma) decay
Transformation of
dysprosium
nucleus in
excited state
The other classes of radioactive decay:
➢ Emission of proton, deuteron, neutron …
➢ Fission of heavy nuclei
Radioactive decay
57
Interaction of ionising radiation with
matter
➢ The interaction of radiation with matter is usually
accompanied by the formation of secondary radiation
which differs from the primary radiation by lower energy
and often also by kind of particles.
➢ Primary or secondary radiation directly or indirectly
ionises the medium, and creates also free radicals.
➢ A portion of the radiation energy is always transformed
into heat.
➢ The energy loss of the particles of primary radiation is
characterised by means of LET, linear energy transfer,
i.e. energy loss of the particle in given medium per unit
length of its trajectory. The higher the LET the more
damaging is the radiation to tissues and the higher the
risk from the radiation.
58
Attenuation of X / gamma radiation
When a beam of X or gamma radiation passes through a substance:
absorption + scattering = attenuation
A small decrease of radiation intensity -dI in a thin substance layer is
proportional to its thickness dx, intensity I of radiation falling on the layer,
and a specific constant m:
-dI = I.dx.m
After rewriting:
dI/I = -dx.m
After integration:
I = I0.e-m.x
I is intensity of radiation passed through the layer of thickness x, I0 is the
intensity of incident radiation, m is linear coefficient of attenuation [m-1]
(depending on photon energy, atomic number of medium and its density).
Interaction of ionising radiation with matter
x
59
Interactions of photon radiation (X-rays
and gamma rays)
➢ Photoelectric effect and Compton scattering – see the lecture on Xray
imaging.
➢ Electron - positron pair production (PP) – very high energy photons
only. The energy of the photon is transformed into mass and kinetic
energy of an electron and positron. The mass-energy E in each particle
is given by:
E = m0 c2 (= 0,51 MeV),
m0 is rest mass of an electron / positron (masses of electron and
positron are equal), c is speed of light in vacuum. Energy of the photon
must be higher than twice the energy calculated using the above formula
(1.02 MeV). We can write:
E = h.f = (m0.c2 + Ek1) + (m0.c2 + Ek2)
➢ Terms in brackets: mass-energies of created particles, Ek1 a Ek2 kinetic
energies of these particles.
➢ The positron quickly interacts (annihilates) with any nearby electron, and
two photons originate, each with energy of 0.51 MeV.
Interaction of ionising radiation with matter
60
Electron - positron pair production
Interaction of ionising radiation with matter
61
Interaction of corpuscular radiation with
tissue
➢b radiation = fast electrons or positrons – ionise the medium as in Xray
production. Trajectory of a b particle is several millimetres in
aqueous medium.
➢a radiation ionises directly by impacts. There is formed big number of
ions along its very short trajectory in medium (mm) – so it loses energy
very quickly along a short trajectory (= very high LET) .
➢Neutrons ionise by elastic and non-elastic impacts (scatter) with
atomic nuclei. The result of an elastic scatter differs according to the
ratio of neutron mass and atom nucleus mass. When a fast neutron
hits the nucleus of a heavy element, it bounces off almost without
energy loss. Collisions with light nuclei lead to big energy losses. In
non-elastic scatter, the slow (moderated, thermal) neutrons
penetrate into the nucleus, and if they are emitted from it again, they do
not have the same energy like the incident neutrons. They can lead to
the emission of other particles or fission of heavy nuclei.
Interaction of ionising radiation with matter
62
Main quantities and units for
measurement of ionising radiation
➢Absolute value of particle energy is very small. Therefore, the
electron volt (eV) was introduced. 1 eV is the kinetic energy of an
electron accelerated from rest by electrostatic field of the potential
difference 1 volt.
1 eV = 1.602×10-19 J.
➢Energy absorbed by the medium is described by absorbed dose (D)
- unit gray, Gy). It is the amount of energy absorbed per unit mass of
tissue. Gray = J.kg-1
➢Dose rate expresses the absorbed dose in unit time [J.kg-1.s-1]. The
same absorbed dose can be reached at different dose rates during
different time intervals.
➢The radiation hazard to biological objects depends mainly on the
absorbed dose and the type of radiation. The radiation weighting
factor is a number which indicates how hazardous a type of radiation is
(the higher the LET the higher the radiation weighting factor).
➢Equivalent dose De is defined as the product of the absorbed dose
and the radiation weighting factor. The unit of Equivalent dose is the
sievert (Sv).
Interaction of ionising radiation with matter
63
Biological effects of ionising radiation
➢ Physical phase – time interval of primary effects. Energy of
radiation is absorbed by atoms or molecules. Mean duration
is about 10-16 s.
➢ Physical-chemical phase – time interval of intermolecular
interactions (energy transfers). About 10-10 s.
➢ Chemical (biochemical) phase – free radicals are formed.
They interact with important biomolecules, mainly with DNA
and proteins. About 10-6 s.
➢ Biological phase – a complex of interactions of chemical
products on various levels of the living organism and their
biological consequences. Depending on these levels, the
duration ranges from seconds to years.
64
Biological effects of ionising radiation
➢ Direct action (hits) – physical and physical-chemical
process of radiation energy absorption, leading directly
to changes in important cellular structures. It is the most
important action mechanism in cells with low water
content. Theory of direct action is called target theory. It
is based on physical energy transfer.
➢ Indirect effects are mediated by water radiolysis
products, namely by free radicals H* a OH*. It is most
important in cells with high water content. The free
radicals have free unpaired electrons which cause their
high chemical reactivity. They attack chemical bonds in
biomolecules and degrade their structure. Theory of
indirect action – radical theory – is based on chemical
energy transfer.
65
Effects on the cell
In proliferating cells we find these levels of
radiation damage:
➢ Transient stopping of proliferation
➢ Reproductive death of cells (vital functions are
maintained but proliferation ability is lost)
➢ Instantaneous death of cells
Cell sensitivity to ionising radiation
(radiosensitivity), or their resistance
(radioresistance) depends mainly on the repair
ability of the cell.
Biological effects of ionising radiation
66
Effects on the cell
Factors influencing biological effects in general:
➢ Physical and chemical: equivalent dose, dose rate,
temperature, spatial distribution of absorbed dose, presence of
water and oxygen.
➢ Biological: species, organ or tissue, degree of cell
differentiation, physiological state, spontaneous ability of repair,
repopulation and regeneration.
Sensitivity of cells is influenced by:
➢ Cell cycle phase (S-phase!)
➢ Differentiation degree. Differentiated cells are less sensitive.
➢ Water and oxygen content. Direct proportionality (+,+)
Very sensitive are e.g. embryonic, generative, epidermal, bone
marrow and also tumour cells
Biological effects of ionising radiation
67
Tissue sensitivity
lymphatic
spermatogenic epithelium of testis
bone marrow
gastrointestinal epithelium
ovaries
cells of skin cancer
connective tissue
liver
pancreas
kidneys
nerve tissue
brain
muscle
Arranged according to the
decreasing radiosensitivity:
Typical symptoms of radiation
sickness:
1. Non-lethal – damage to the
erythropoiesis (bone marrow),
effects on gonads
2. Lethal – gastrointestinal
syndrome (damaged
epithelium), skin burning,
damage to suprarenal glands,
damaged vision, nerve
syndrome (nerve death)
Late sequels – cumulative –
genetic damage, cancer
Biological effects of ionising radiation
The the most unique devices in Czech republic
• The Lexell gamma knife – Praha, Bulovka from 1992
• The Cyberknife Ostrava - robotic linear accelerator
• Proton therapy centrum Praha
68
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Authors:
Vojtěch Mornstein, Ivo Hrazdira, Vladan Bernard
Content collaboration and language revision:
Carmel J. Caruana
Presentation design:
Lucie Mornsteinová
Last revision: March 2015